semiconductor diode

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下面我们来构造第一个半导体应用，二极管，只需要把n-type和p-type连接起来即可，是不是很简单。只有简单的基础件，才能更好的“集成”。

depletion region1

When the p-type and the n-type materials are kept in contact with each other, the junction between them behaves differently from either side of the material alone. The electrons and holes are close to each other at the junction. According to coulomb’s law, there is a force between the negative electrons and the positive holes. When the p-n junction is formed a few electrons from the n-type diffuse through the junction and combines with the holes in the p-side to form negative ions and leaves behind positive ions in the n-side. This results in the formation of the depletion layer, which acts as the barrier and does not allow any further flow of electrons from the n region to the p region.

No Applied Bias(V = 0V)

no-bias

在没有外部电压的情况下，depletion region正常存在。n type这边主要载流子是电子，但是如果要流向p type，需要克服正电子的吸引，所以只有一小部分能够过去，这个数量和从p type流过来的电子（少数载流子）数目接近，也就是图12 c 左上的和右下的正好差不多抵消。同理两个也差不多。所以总体电流为0。

In the absence of an applied bias across a semiconductor diode, the net flow of charge in one direction is zero.

Reverse-Bias Condition()

reverse-bias

在反向电压的情况下，n type里面的电子会被“抽走”，所以原来图12 c右下的向右的会几乎为0。depletion region会加厚。p type的不会有影响，所以存在的电流就是 Minority-carrier flow.

The current that exists under reverse-bias conditions is called the reverse saturation current and is represented by .

Foward-Bias Condition()

foward-bias

当正向电压的时候，首先depletion region会变薄，因为n type这边会有大量电子注入，重新和正电子结合，p type的电子会被“抽走”。当电压加到一定程度，突然大量电子从n涌入p，图12 c 右下的是会不断增大。

  • is the reverse saturation current
  • is the applied forward-bias voltage across the diode
  • n is an ideality factor, which is a function of the operating conditions and physical construction; it has a range between 1 and 2 depending on a wide variety of factors (n =1 will be assumed throughout this text unless otherwise noted).

  • k is Boltzmann’s constant =
  • is the absolute temperature in kelvins = 273 + the temperature in
  • q is the magnitude of electronic charge =
diode-characteristics

虚线是理想的曲线，实现是实际的情况。

The actual reverse saturation current of a commercially available diode will normally be measurably larger than that appearing as the reverse saturation current in Shockley’s equation.

反向的饱和电流实际会在理想的下方，主要原因是：

  • – leakage currents

  • – generation of carriers in the depletion region

  • – higher doping levels that result in increased levels of reverse current

  • – sensitivity to the intrinsic level of carriers in the component materials by a squared

    factor—double the intrinsic level, and the contribution to the reverse current could

    increase by a factor of four.

  • – a direct relationship with the junction area—double the area of the junction, and

    the contribution to the reverse current could double. High-power devices that have

    larger junction areas typically have much higher levels of reverse current.

  • – temperature sensitivity—for every 5°C increase in current, the level of reverse sat- uration current in Eq. 1 will double, whereas a 10°C increase in current will result in

    doubling of the actual reverse current of a diode.